1. Field of the Invention
The present invention relates to an electron beam apparatus using electron emission, an image forming apparatus using the electron beam apparatus, and a component for the electron beam apparatus, and also relates to methods of manufacturing these apparatuses and component.
2. Related Background Art
Two types of electron emitting elements are known, hot cathode elements and cold cathode elements. As the cold cathode element, a surface conductivity type electron emitting element, a field emission type element (hereinafter abbreviated as FE type), a metal/insulator/metal type electron emitting element (hereinafter abbreviated as MIM type) are known.
The surface conductivity type electron emitting element utilizes the phenomenon that as current flows through a thin film small area formed on a substrate in parallel to the film surface, electrons are emitted. Surface conductivity type electron emitting elements heretofore reported include an element using an SiO.sub.2 thin film proposed by Elinson et aL (M. I. Elinson, Radio Eng. Electron: Phys., 10, 1290 (1965)), an element using an Au thin film (G. Dittmer: "Thin Solid Films", 9, 317 (1972), an element using an In.sub.2 O.sub.3 /SnO.sub.2 thin film (M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf", 519 (1975), and an element using a carbon thin film (Hisashi ARAKI et al, "Vacuum", Vol. 26, No. 1, 22 (1983).
As a typical example of the structure of a surface conductivity type electron emitting element, the element proposed by M. Hartwell et al is shown in the plan view of FIG. 12. In FIG. 12, reference numeral 1 represents a substrate, and reference numeral 2 represents a conductive thin film made of metal oxide formed through sputtering. The conductive thin film 2 is patterned to have an H-character shape as shown in FIG. 12. An electron emitting portion 3 is formed by subjecting the conductive thin film 2 to an energization process called an energization forming process.
The energization forming process forms the electron emitting portion by using an electric power. With this process, a constant d.c. voltage or a d.c. voltage very gradually raising its amplitude in the order of, for example, about 1 V/min is applied across opposite ends of the conductive thin film 2 to locally break, deform, or decompose the conductive thin film 2 to thereby form the electron emitting portion 3 having a high electrical resistance. Part of the conductive thin film 2 locally broken, deformed or decomposed has cracks so that as an appropriate voltage is applied to the conductive thin film 2, electron s are emitted near at the cracks.
Examples of FE type elements are disclosed, for example, in "Field Emission", Advance In Electron Physics, 8, 89 (1956) o r C. A. Spirndt, "Physical Properties of Thin-Film Field Emission Cathodes with molybdenum Cones", J. Appl. Phys. 47, 5248 (1976).
As a typical example of the structure of an FE type element, the element proposed by C. A. Spindt et al is shown in the cross sectional view of FIG. 13. In FIG. 13, reference numeral 4 represents a substrate, reference numeral 5 represents an emitter wiring layer made of conductive material, reference numeral 6 represents an emitter cone, reference numeral 7 represents an insulating layer, and reference numeral 8 represents a gate electrode. With this element, as an appropriate voltage is applied across the emitter cone 6 and gate electrode 8, electrons are emitted from the tip of the emitter cone 6 through field emission.
Another example of the FE type element has an emitter and a gate electrode disposed on a substrate generally in parallel to the substrate surface, without incorporating the lamination structure shown in FIG. 13.
An MIM type element is disclosed, for example, in C. A. Mead, "Operation of Tunnel-emission Devices", J. Appl. Phys., 32, 646 (1961). A typical example of the MIM type element is shown in the cross sectional view of FIG. 14. In FIG. 14, reference numeral 9 represents a substrate, reference numeral 10 represents a lower electrode made of metal, reference numeral 11 represents a thin insulating film having a thickness of about 80 to 300 angstroms, and reference numeral 12 represents an upper electrode made of metal having a thickness of about 80 to 300 angstroms. With the MIM type element, as an appropriate voltage is applied across the upper and lower electrodes 12 and 10, and electrons are emitted from the surface of the upper electrode 12.
As compared to the hot cathode elements, the cold cathode elements described above can emit electrons at a low temperature and do not require a heater. Therefore, the cold cathode element has the structure simpler than the hot cathode element, a fine element can be manufactured, and even if a number of elements are disposed on a substrate at a high density, a problem of thermal melting of the substrate and the like does not occur. As different from a hot cathode element operating with a heated heater and therefore with a slow response speed, the cold cathode element has an advantage of a fast response speed. The application field of the cold cathode element includes an image forming apparatus such as an image displaying apparatus and an image recording apparatus, an electron beam source, and the like.
As an example of the application of a cold cathode element to an image displaying apparatus, image displaying apparatuses proposed by the present assignee and disclosed in U. S. Pat. No. 5,066,883 and Japanese Patent Laid-Open Application Nos. 2-257551 and 4-28137 are known. These image displaying apparatuses use a combination of surface conductivity type electron emitting elements and a fluorescent film which generates light upon impingement of an electron beam. As an example of the application to an image displaying apparatus using a number of FE type elements, a flat plane type display apparatus reported by R. Meyer et al is known (R. Meyer, "Recent Development on Micro-tips Display at LETI", Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6 to 9 (1991)). An example of the application to an image displaying apparatus using a number of MIM type elements, is disclosed in Japanese Patent Laid-Open Application No. 3-55738 filed by the present assignee.
The surface conductive type electron emitting element in particular has a simple structure and is easy to manufacture. It has therefore an advantage that a number of elements can be easily formed in a large area. As compared to a liquid crystal display, an image displaying apparatus using a combination of surface conductivity type electron emitting elements and a fluorescent film does not require a back light because of its self-light-emission type and is excellent in a broad angle of view.
In a flat plane type image displaying apparatus, a number of electron emitting elements are disposed on a flat substrate, and a fluorescent member generating light upon impingement of electrons is disposed facing the flat substrate. The electron emitting elements are disposed on the substrate in a two-dimensional shape (the elements are called a multi-electron-beam source). Each element is connected to row and column direction wiring lines. One method of driving elements is a simple matrix drive method. In order to emit electrons from an element on a desired row of the matrix, a select voltage is applied to the row and synchronously with this, a signal voltage is applied to the column wiring line. Electrons emitted from the electron emitting element at the selected row are accelerated toward the fluorescent member and excite it to generate light therefrom. By sequentially applying the select voltage to each row, an image can be displayed.
It is necessary to maintain a vacuum in the space between a substrate (rear plate) on which electron emitting elements are formed in the two-dimensional matrix shape and the substrate (face plate) on which a fluorescent member and an acceleration electrode are formed. Since an atmospheric pressure is applied to the rear and face plates, the substrate having a thickness resistant to the atmospheric pressure become necessary, the more the displaying apparatus becomes large. However, the thick substrate increases the weight of the displaying apparatus. In view of this, support members (spacers) are inserted between the rear and face plates to maintain the distance between the rear and face plates and prevent breakage of the rear and face plates.
The spacer is required to have a mechanical strength sufficient for being resistant to the atmospheric pressure, and also required not to greatly affect the orbit of electrons flying between the rear and face plates. The reason of influencing the electron orbit is charged on the spacer. Charges on the space may be ascribed to that part of electrons emitted from the electron source or electrons reflected from the face plate become incident upon the spacer and secondary electrons are emitted from the spacer or ions generated by collision are attached to the spacer surface.
As the spacer is charged positive, electrons flying near the spacer are attracted to the spacer so that a displayed image near the spacer has a distortion. The influence of charges becomes conspicuous as the distance between the rear and face plates becomes large.
Generally, charges are suppressed by imparting a conductivity to the charge surface to flow some current therethrough. This concept was introduced into the spacer and the space surface was coated with tin oxide, which is disclosed in Japanese Patent Laid-Open Application No. 57-118355. A method of coating the spacer with PbO containing glass is disclosed in Japanese Patent Laid-Open Application No. 3-49135.
In improving a creeping discharge breakdown voltage, it is effective if the spacer surface is coated with material having a small secondary emission ratio. As an example of a material having a small secondary emission ratio coated on the spacer surface, chromium oxide (T. S. Sudarshan and J. D. Cross: IEEE Trans. EI-11, 32 (1976) and copper oxide (J. D. Cross and T. S. Sudarshan: IEEE Trans. EI-9, 146 (1974) are known.